The overall goal of this proposal is to analyze, at the molecular level, the interaction between virus and the host cell and resulting pathogenesis. Analysis of the virus-mediated signal transduction pathway that results in changes in the expression of cellular genes is focused on the interferon (IFN) genes. In the initial stages of this grant, IFNA and IFNB were cloned and characterized and virus-mediated expression of these genes has been studied in both in vitro and in vivo. During the present funding period, it was shown that viral infection and a low molecular weight inducer, imiquimod, induce similar sets of cytokine genes and employs similar signal transduction pathway. Induction of IFNA and IFNB genes employs unique mechanisms. Nuclear factors binding to a novel DNA element (AF-1) essential for expression of IFNA genes in mice were identified. These studies led to an identification of a novel gene, IFN regulatory factor-3 (IRF-3), a member of the IRF family that encodes a protein binding to IFN-stimulated regulatory element (ISRE) and activating ISRE containing promoters. It is our hypothesis that IRF-3 represents a novel, essential element in the virus and/or IFN-induced signal transduction pathway not recognized previously. Furthermore, a novel gene, If-1L, was identified that is located on chromosome 3 in the If-1 locus that modulates IFN induction in mice. During the next funding period, in Aim #1, the role of IRF-3 in virus- and cytokine-mediated signal pathway will be analyzed. This will be done by characterization of the IRF-3 protein and examination of its interaction with other members of the IRF-1 and Stat families, as well as with other cellular proteins. Aim #2 is designed to characterize the macrophage-specific If-1L gene, the protein-encoded by this gene, determine its cellular localization, and examine its ability to modulate IFN expression. Lastly, in Aim #3, the virus-mediated signal transduction pathway leading to the induction of IFN and inflammatory genes will be dissected. Imiquimod will be used as ligand to isolate the protein that may be a target in the signal transduction pathway. The role of JAK-Stat pathway in the induction of IFN genes will be determined. Knowledge of the regulation of IFN gene expression and its dependence on genetic factors is essential for our understanding of the IFN system in mart, where deletion (or defect) in IFN genes can be often found in tumor cells and aberrant expression can be associated with pathogenicity in viral infections and autoimmune diseases. In addition, this study will provide a more rational basis for the possible therapeutic manipulation of the expression of IFN and cytokine systems in man.